1. Field of the Invention
The present invention relates to a semiconductor memory device and, for example, relates to a reading operation of a NAND-type flash memory.
2. Description of the Related Art
A NAND-type flash memory has been known as a non-volatile semiconductor memory. In the NAND-type flash memory, a method of sensing a current is known as a method of reading data. Such a technique is disclosed, for example, by Jpn. Pat. Appln. KOKAI Publication No. 2006-107709.
According to the technique, an influence of noise between bit lines is reduced by maintaining the potential of bit lines constant. However, in order to maintain the potential of bit lines constant, it is necessary to continue to flow a cell current from bit lines to source lines. Then, if the size of one page is, for example, several Kbytes, the total of cell currents will be a very large value of about 100 mA. Thus, there is a possibility that the total of cell currents exceeds current specific permitted for one chip, leading to lower reliability as a product.